I also have the Fatal1ty B450 Gaming-ITX/ac and its performance depends on the bios version.
I had a 2600 in it before dropping a 3600 in. Bios version 3.30 with AGESA Combo-AM4 1.0.0.1. CPU worked fine, forgot exactly what I tried but it didn't like high speed ram and I ran 3000 modules in it at the time.
Bios version 3.40 came out, AGESA Combo-AM4 1.0.0.3. Wow, it's like a different system. I put it in another thread, but I had it working with HyperX 4000 kit at both 3600 and 4000 XMP profiles, and was able to reduce latency even further.
I see bios version 3.50 with AGESA Combo-AM4 1.0.0.3 ABB is out today. I love the description "Improve Destiny2 gaming experience with Matisse CPU.". We're getting game ready bios updates now? I've lost track of all the little changes but hopefully this will help also. In a quick search I found a TPU article claiming it resolves WHEA Error 17 relating to using M.2 PCIe drives. Tom's Hardware says on Gigabyte it removes PCIe 4.0 support from older chipsets.